For many years, Tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV) were the two major tobamoviruses that seriously affected tomato production worldwide.
These seed-borne and mechanically transmitted viruses are difficult to control.
The most effective disease management has been the use of disease-resistant tomato cultivars.
Since the first discovery of Tomato mottle mosaic virus (ToMMV) on tomato from Mexico in 2013, this virus has been identified in Florida and New York in the US as well as in several other countries (i.e., Brazil, China, and Israel). With the high sequence identity of approximately 85% to ToMV and 80% to TMV, there is a need to characterize their serological and biological relationships.
In enzyme-linked immunosorbent assay (ELISA), both TMV and ToMV antibodies strongly cross-reacted with ToMMV. Such serological cross-reactivity was also confirmed when ToMV immunostrips were used to test ToMMV-infected samples.
To evaluate whether the emerging ToMMV could break the disease resistance of tomato cultivars that were used for breeding resistance to TMV and ToMV, three commercial tomato cultivars were screened along with the control 'Moneymaker' in a greenhouse through mechanical inoculation. 'Moneymaker' was susceptible to all three tobamoviruses, but showed some recovery (tolerance). Cultivar 'E' was fully resistant and cultivar 'I' was fully susceptible to all three tobamoviruses, but the reaction of cultivar 'B' was more complicated.
Cultivar 'B' offered full resistance to TMV and ToMV, but only a partial resistance to ToMMV, resulting in a segregating population.
This resistance breaking in cultivar 'B' by the emerging ToMMV is a serious concern to tomato growers.
The mechanism of such resistance breaking has yet to be determined.